Emission reduction of carbon dioxide (CO2 gas) as heat-trapping gas has recently become a worldwide theme, and emission reduction of carbon dioxide has been also strongly required to vehicles as discharging sources of carbon dioxide. Therefore, reduction of the friction between a sliding member and a slid member as a sliding partner material in a vehicle has been attempted. For example, it has been found that enhancement of fuel consumption, prevention of baking and prevention of occurrence of strange noise can be performed by subjecting the sliding surface of a piston (sliding member) of an internal combustion engine to a surface treatment.
As this type of surface treatment method has been proposed a method of infiltrating an aluminum (containing aluminum alloy) base member in chemical conversion coating liquid containing etching liquid and water-soluble metal salt to conduct a surface roughening treatment on the surface of the aluminum base member with the etching liquid, and substantially at the same time, forming metal coating on the surface of the aluminum base member with the metal constituting the water-soluble metal salt (see Patent Document 1, for example).